Electromagnetic railguns (EMR) are generally known in the prior art. A typical railgun includes at least one pair of oppositely spaced generally parallel electrically conducting rails. The breech ends of the rails are connected to a source of strong pulsed current. A projectile is placed between the rails. To accelerate the projectile, a conductive solid armature or a plasma armature is used. When the current pulse is applied to the rails, the armature completes the current path between the rails, and, as those skilled in the art will appreciate the armature and projectile are accelerated by the force jxB.
In solid conductive armature railguns, one of the factors limiting the achievable velocity is the Joule heating of the armature. However, through use of a high conductive metallic armature (copper, for example) a very high velocity might be achieved before it begins to melt if the current in the armature were uniform.
In practice, however, a partial melting and vaporization of the metal armature (and subsequent transition to the plasma armature regime of acceleration) usually occurs after the solid armature has been accelerated to a certain critical velocity, typically on the order of 1 km/s. By using a plasma armature regime, the projectile can be further accelerated. However, numerous studies have shown that there exists a certain critical velocity, typically 6-7 km/s, for the plasma armature method of acceleration. Near this critical velocity most of the driving force is used to involve into motion new portions of material ablating from the rails and isolator walls of the bore, thus no further increase of the projectile velocity occurs. Thus, it is important to understand causes of the failure of the solid armature regime and to find suitable means to prevent it.
Both theoretically and experimentally it has been shown that an intense melting and vaporization of the solid armature material occurs due to high concentration of current in a small region near the rear end of the contact zone between the solid armature and each of the rails. This phenomenon--the "velocity skin effect"--has much in common with the conventional "skin effect" for pulsed current, and is caused by the slow diffusion of the magnetic field in the high conductive rails which are ordinarily used in the railguns.
Another cause of intense ablation and erosion of the armature and rails may be connected with a loss of electromechanical contact between the solid armature and rails due to gaps. The gaps may appear, in particular, due to displacements of the rails caused by strong magnetic repulsion of opposite currents in the rails. The current then passes through the gaps (between the armature and rails) in the regime of gas discharge. The energy dissipated in the gas discharge overheats the surfaces of the rail and armature due to heat conduction and intensive radiation. As a result, a plasma armature may appear.
On the other hand, excessive tightening of the electromechanical contact to ensure the contact between rails and solid armature may result in increased friction losses, overheating of the rail and armature contacting surfaces, and gouging of the armature and rails at high relative velocity. Further, increasing the stiffness of the rails typically involves making the railgun barrel more massive and complex.
Thus, it will be appreciated by those skilled in the art that to develop an effective armature/rail combination and a barrel design, several various requirements and design considerations should be simultaneously met and taken into account. First, it is important to virtually avoid gaps between the rails and the armature appearing due to magnetic forces. Second, at the same time the contact between the armature and rails should be kept moderately tight. Third, it is important to avoid significant current concentration due to the velocity skin effect.
Several approaches have been presented previously which were partial solutions to these problems. In particular, it has been recommended to diminish rail displacements, and thus to reduce gaps, by increasing the stiffness of the railgun barrel. Also, several approaches have been aimed at improving the electromechanical contact and to diminish current concentration by providing:
(a) flexible trailing ends of the armature; PA1 (b) wire contactors at the side or at the trailing edge of the armature; PA1 (c) a chevron shaped armature, consisting of intermittent laminas of highly conductive and highly resistive materials; and PA1 (d) compounded rails including high resistive layers on the contact side of the rail, with the thickness increasing from the breech end to the muzzle end of a barrel.
However, none of the prior art has accomplished each of the desired goals. Therefore, there arises a need for a railgun which is capable of reducing local current densities to reduce arcing and reducing the need for massively solid/rigid rails. The present invention directly address and overcomes the shortcomings of the prior art.